Method and apparatus for detecting impending earthquakes

ABSTRACT

An apparatus and associated method for detecting impending earthquakes includes at least one sensor, and preferably multiple sensors, for mounting on a building or other like structure, and include a transducer for converting vibration signals to electronic impulses. The signals are transmitted to a solid state detection circuit, which distinguishes between extraneous signals and signals indicative of the P-waves which signal an impending earthquake. Discrimination between relevant and non-relevant may be achieved by selecting a minimum amplitude and duration of signals within a selected frequency range, and triggering an alarm when the selected minimums are exceeded. Where multiple sensors are deployed, temporal overlap between selected signals can be assessed for further discrimination.

This application is 371 of PCT/CA98/00531 filed Jun. 1, 1998 whichclaims benefit of U.S. provisional application No. 60/056,363 filed Aug.19, 1997.

FIELD OF THE INVENTION

The present invention is directed to detection of impending earthquakesand more particularly, the invention relates to a detector and methodfor discriminating between general earth tremors and tremors which areprecursors to an earthquake. Further, the invention relates to arelay-type earthquake detector for relaying a warning signal to remotelylocated sensors.

BACKGROUND OF THE INVENTION

It is well documented that earthquakes have characteristic wave formsand vibration characteristics which are particularly useful foridentifying earthquake caliber vibrations from simple random vibrationswhich are typically encountered in earth formations. Typically, anearthquake tremor results in the propagation of P-(primus) waves, whichare propagated as compression and rarefaction and as well involvesS-waves (secundus), which waves propagate an orthogonal angle to thedirection of the wave. Generally speaking, the P-waves have a naturalfrequency of approximately 5 Hertz(Hz) while S-waves have a frequencysignificantly less than the P-waves. The S-waves have a significantlylarger amplitude than the P-waves and therefore are the waves that areprincipally involved in the destruction to structures. P-waves typicallytravel at a faster rate from an epicenter to a given locale incomparison with S-waves. Thus, detection of P-waves can serve as awarning of the arrival of S-waves at a given location, in particular alocation at some remove from the epicenter.

One of the primary difficulties in earthquake detection relates to thetime factor involved in detecting tile P-waves. As will be realized, ifP-waves can be detected as early as possible, this provides time forevacuation etc., of a building or area in order to avoid potential humaninjury caused by the arrival of S-waves which, as indicated above, arethe chief destructive waves transmitted by geological formations. Earlydetection of P-waves has conventionally been difficult.

The art has previously proposed various detectors and other arrangementsto measure P-waves to portend S-waves. However, in existingarrangements, one of the primary difficulties is providing sensitivitysufficient to detect P-waves at a distance from the epicenter of anearthquake without incurring large costs. A further difficulty has beenencountered in that there is often difficulty resolving false alarmsfrom a real earthquake, due to interference in the instrumentation byextraneous vibrations or other frequencies. It is desirable to provide adetector capable of discriminating between P-waves and ordinary,everyday ground and building tremors unrelated to an earthquake. Inparticular, detectors mounted to a building should be capable ofdiscriminating between the natural vibration frequencies of the buildingstructure, which are a function of the structure, and frequenciesindicative of P-waves. The same may be accomplished by means of aninformation processing unit that stores vibration data and is programmedto discriminate between frequently occurring frequencies andnon-regularly occurring frequencies within the range of P-waves.

Typical of the art that has been patented in this field is U.S. Pat. No.4,689,997, (Windisch). The reference provides a detector which primarilyemploys a vertical spring barb mounted on a support. A coupler issupported on the other end of the barb and this coupler is connectedthrough a coil spring to a mass positioned in concentricity with thebarb and coupler. The spring and mass components are selected to have anatural resonant frequency corresponding to that of an earthquake tremoror other vibration to be detected. A switching circuit is provided todetonate an alarm once the earthquake frequency is detected. Windischdoes not provide an integrated circuit mechanism for detection of earthtremors, but rather relies on a mechanical arrangement in the form of aspring and mass system. As is known, such systems are susceptible totemperature fluctuations which can alter the point at which theapparatus can detect the earthquake frequency. Further, the Windischarrangement does not appear to provide a system which discriminatesbetween simple extraneous vibration and earthquake caliber frequencies.

Caillat et al., in U.S. Pat. No. 5,101,195, provide a discriminatingearthquake detector. The arrangement relies on an electromechanicalarrangement having a cantilevered device with a predetermined mass onone end. During movement of the beam, an electrical signal is generatedwhich, in turn, is useful for detection of P- and S-waves. Similar tothe above-mentioned detectors in the prior art, the arrangement providedin this reference would appear to have limited utility in that there isno provision for a comparison between earthquake caliber waves and thosewhich are simply extraneous, such as would be encountered in trafficvibration, mechanical vibration in a building, aircraft vibration, etc.

U.S. Pat. No. 5,001,466, issued Mar. 19, 1991 to Orlinsky et al.,provides an earthquake detector employing an electrically conductiveliquid switch means among other variations thereof.

In view of what has been previously proposed in the art, it is clearthat there exists a need for a more sophisticated earthquake detectorwhich is discriminatory between extraneous vibration and earthquakelevel vibration which is not limited in sensitivity.

A further need is for a detector having the ability to communicate bothwith other like detectors or servers, in order to improve detectioncapabilities, and remote locations for coordination of earthquakeinformation.

Accuracy of a detector may also be enhanced by having regard to variousP-wave characteristics. For example, it has been found that P-waves areindicative of serious earthquakes if they have a duration greater than acertain value. For most locations, this value is approximately 15milliseconds, although in some locations this is less. Further, it hasbeen found that earthquakes may be predicted with reasonable accuracy ifmultiple spaced-apart sensors detect P-waves over tile temporalthreshold with temporal overlap existing between the detected P-waves.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an improved earthquakedetector capable of detecting earth tremors at a selected frequency andverifying whether the same are indicative of an imminent earthquake. Afurther object is to provide a detector system comprising a centralprocessor in communication with multiple spaced apart sensors to furtherenhance advance warning of an earthquake.

Another object of the present invention is to provide an improveddiscriminatory earthquake detector for discrimination against naturalstructural vibrations.

Another object of the present invention is to provide a method ofdetecting vibration signals indicative of an earthquake, comprising thesteps of:

providing a vibration detecting means for detecting vibration signals ina structure responsive to ground vibration, the detection meanscomprising an integrated circuit including a potentiometer circuit;

mounting the detecting means to the structure;

determining the natural vibration frequencies of the structure;

intermittently comparing electronically any extraneous vibration signaldifferent from the vibration signal of the structure; and

determining whether the extraneous signal is within a predeterminedearthquake signal level indicative of P-waves.

The step of determining whether the signal is indicative of P-waves mayinclude measuring electronically the amplitude and duration of thevibration signals and determining whether these exceed predeterminedminimum levels.

A further object of the present invention is to provide a method fordetecting an earthquake, comprising the steps of: providing anearthquake detector having a first sensor for sensing a selectedfrequency indicative of an earthquake and a transducer means fortransmitting and receiving information and an alarm;

providing a second sensor independent of the first for at leastreceiving information from the first sensor, the second sensor forverifying information received from the first sensor;

subjecting the first and second sensors to the selected frequency;

transmitting information indicative of the detected frequency from thefirst server to the second sensor;

processing the information by the sensors; and

activating the alarm means when the frequency is indicative of anearthquake.

Alternatively, the first and second server may independently transmitthe vibration detection information to an independent control unit.

In a further aspect, the method comprises the steps of:

providing first and second sensors remotely positioned from each otherfor sensing a selected vibration frequency indicative of an impendingearthquake;

providing communication means for communication between the first andsecond sensors;

providing a processing unit in communication with the first and secondsensors for selecting earth tremor information received from the sensorsin the form of a voltage having an amplitude;

subjecting the sensors to the selected frequency and communicating theinformation indicative of the vibration between the sensors;

selecting within the processing unit a voltage peak indicative ofvibrations having an amplitude and duration exceeding selected minimumlevels;

assessing any temporal overlap between the selected voltage peaksassociated with each of the sensors,

activating alarm means when the amplitude, temporal duration andtemporal overlap of the voltage peaks associated with the sensors isindicative of an impending earthquake. Communication between the sensormeans and processing unit may be affected by means of wireless or wiredelectronic communication means, including wireless communication in theinfrared or radio frequencies.

Optionally, the processing unit may be remotely positioned from thefirst and second sensors, and itself incorporate a third sensor.

Conveniently, information from the processing unit can be downloaded toa computer programmed to process the information and optionally transmitthe information to corresponding earthquake detectors.

Optionally, the sensors and processing unit can communicate by means oflight-emitting diodes (LED's), or at radio, microwave or IR frequencies.

A further object of the present invention is to provide an integratedcircuit electronic detector for detecting any vibration signals of astructure or structures positioned on a substrate, comprising:

detector means for detecting a predetermined vibration signal of thestructure and an extraneous signal different from the vibration signal;

amplifier means for amplifying the signal;

comparator means for comparing an extraneous signal with thepredetermined vibration signal of the structure to verify whether theextraneous signal is indicative of P-waves; and

potentiometer signal adjustment means for adjusting the detector meansto different vibration signals of a structure.

Selectively actuable alarm means may be connected to the comparatormeans, the alarm means capable of actuation when the extraneous signalis within the predetermined vibration signal.

In a further aspect, the comparator means includes a filter for limitingthe detection to vibrations having an amplitude greater than apredetermined minimum and a timer for measuring the duration of saidamplitude peaks. The alarm is triggered when the duration of anamplitude peak exceeds a selected amount. For many locations, thisselected duration is about 15 milliseconds.

A further object of the present invention is to provide an apparatus fordetecting earthquakes and relaying a signal generated therefrom to aremote location, comprising:

an earthquake detector having a first sensor for detecting a frequencyindicative of an earthquake and an alarm means actuable at thefrequency;

transducer means for relaying and receiving information from the firstsensor;

second sensor means remote from the first sensor including a secondtransducer means for communicating at least with the first sensor; and

a comparator means associated with the earthquake detector for comparinga transmitted signal received by the first sensor with the second sensorfor confirmation of an earthquake signal.

The sensors may be linked by any known means for transmissions ofelectronic signals, including wire linkage and wireless linkage. Thelatter may include, for example, infrared and radio frequencytransmission, for example in the 800-900 megahertz range.

In a further aspect, communication links are established between theunits in at least two different frequencies.

In a further aspect, information from the sensors is processed in alogic device for recording vibration information in order to betterdiscriminate against unimportant vibrations, and interfacing with thealarm means for providing an alarm in advance of an earthquake.

In a further aspect, a detector is provided for detecting precursorearthquake tremors, comprising:

first and second sensors for detecting vibrations at a frequencyindicative of an impending earthquake;

communication means for transmitting and receiving information betweenthe first and second sensor means;

a comparator means for comparing transmitted signals received by thefirst and second sensors for confirmation of an impending earthquakesignal;

alarm means actuable at the said frequency.

In a further aspect, the apparatus includes a central controller forcontrolling the operation of the sensors. The controller may alsoincorporate information storage means for recording and storingvibration tremor information detected by the sensors. The controller mayfurther include a communications port, such as an RS 232 port,permitting an interface of the controller with a computer, which may beprogrammed with software for storing and processing the earth tremorinformation.

The controller may be independent of the first and second sensors andmay itself incorporate a third sensor.

The transducers within the sensors convert the vibration detected by thesensor into a voltage value, which in turn is transmitted to thecontroller. A voltage peak above a preselected level is indicative ofP-waves affecting the sensor.

The controller preferably includes voltage peak comparison means, forcomparing the duration of a voltage peak above a selected limit,indicating a precursor earthquake tremor detected by both (or all three)sensor means, and for assessing any temporal overlap in the voltagepeak. The controller further includes filter means whereby voltage peakshaving an amplitude above a selected amount are compared for temporaloverlap, and voltage peaks having an amplitude below the selected amountare not so subjected. The controller further conveniently includesadjustment means to permit the user to adjust the selected durationcutoff to reflect local earthquake conditions.

Having thus described the invention, reference will now be made to theaccompanying drawings illustrating the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the apparatus according to oneembodiment;

FIG. 2 is a longitudinal cross-section of the apparatus of FIG. 1;

FIG. 3a is a top plan view of the top mounting plate of the apparatus;

FIG. 3b is a bottom plan view of the mounting bracket;

FIG. 4 is a schematic illustration of the electrical elements accordingto one embodiment of the present invention;

FIG. 5 is a block diagram showing the operation of an apparatus fordetecting earthquake activity, according to one embodiment of thepresent invention;

FIG. 6 is a block diagram showing the operation of an apparatus fordetecting earthquake activity according to a further embodiment of thepresent invention;

FIG. 7 is a block diagram illustrating a third embodiment of theinvention; and

FIG. 8 is a block diagram illustrating a fourth embodiment of theinvention.

Similar numerals in the figures denote similar elements.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, FIG. 1 is one possible embodiment of thediscrete earthquake alarm, broadly denoted by numeral 10. The apparatusincludes a front face 12 with opposed ends 14 and 16 and a rear face 18.A top mounting plate 20, shown in plan view in FIG. 3b, is provided withtwo spaced apart eyelets 22 and 24 for mounting the apparatus 10 to asubstrate such as a building etc. (not shown). A bottom plate 26 isprovided with two apertures 28 and 30. Aperture 28 receives a resetbutton (not shown) in order to reset the circuit discussed hereinafter.Aperture 30 receives a light emitting diode (LED) (not shown), thepurpose of which will be discussed below.

FIG. 2 illustrates a longitudinal cross-section of the apparatus 10 inwhich a piezoelectric alarm element 32 is shown in chain line.Piezoelectric element 32 is designed to produce an audible signal oncethe apparatus in activated indicating an earthquake is imminent. Frontface 12, as illustrated in FIG. 2, includes lips 34 and 36, which arereceived within cooperating recesses 39 and 40, respectively on theapparatus 10.

Referring now to FIG. 4, an example of the circuitry employed in theapparatus 10 is shown in schematic representation. The apparatusprovides a transducer circuit, broadly denoted by numeral 42 fordetecting incoming signals. The incoming signals are filtered by apotentiometer circuit 44 encompassing resistors R1, R2 and potentiometerP1. The potentiometer circuit 44 allows adjustment of a selectedfrequency or frequencies to be introduced into the remaining circuitryand representing the natural harmonics of the building. Once a signalhas been selected, the same can be passed on to the amplificationportion of the circuit, broadly embracing resistors R3, R4, R5 and UARTchip 4 (U4 Voltage Source V_(cc)). The amplification circuit is broadlydenoted by numeral 46. The amplified signal is passed on to a detector48, the detector comprising a UART chip U1A. The detected signal ispassed on to a logic circuit denoted by numeral 50 comprising a pair oflinked UART chips U1B and U1C. The logic circuit compares the signalthat is incoming with tile natural harmonic frequency signal of thebuilding and comparison is made to determine whether the incoming signalis below the predetermined natural frequency of the building. If thesignal does exceed this latter amount, the result is the detonation ofthe alarm to be discussed hereinafter. A manual reset circuit isprovided by the combination of the UART chip U2A and diode D1A, thereset circuit being denoted by numeral 52. Also provided is an automaticreset circuit comprising diode D1B and UART chip U28 and resistor R7.The auto reset circuit is denoted by numeral 54. Automatic reset of thesystem will occur after two minutes of ringing of the alarm. This valveis variable. Numeral 56 represents a conventional clock circuitcomprising a capacitor C2 and resistors R9, R10. The circuit is designedto provide two minutes of ringing of the alarm. Clock circuit 56 isconnected to the main counter chip 58, which acts as the maindistribution system for the circuit. The entire arrangement is connectedto chip 58. Numeral 60 broadly denotes a conventional buzzer or alarmcircuit composed of resistors R16, R17, capacitor C3, UART chips U2D andU2C an Piezoelectric circuit BZ1 as well as diode D7. The buzzer ismodulated by diodes D3A and D3B and together these form the modulationcircuit 62 connected to main counter chip 58.

The apparatus may be adapted to interface with an existing buildingsystem, which may be adapted to trigger the following responses amongothers:

audible alarm

gas supply cut-off

elevator interruption

curtailing of fueling operations

Numeral 64 represents an optional battery check circuit with low voltagedetector lamps to indicate whether the system is operational. This isshown in chain line. The arrangement is provided with diodes D4A, D4B,D5A, D5B and D6 and resistors R13 through R14 as well as transistors Q1,Q2 and light emitting diodes 1/G and 1/R.

In alternate embodiments of the circuit, suitable integrated circuitswhich may be employed include MC14467PI, MC14468P, MC145010DW, all byMotorola, SD2 by Supertex and 5348 by Allegro Electronics. Othersuitable examples will be appreciated by those skilled in the art.

In another embodiment, the clock circuit 56 associated with chip 58 maybe removed as illustrated in chain line in FIG. 4.

With the present invention, it has been found that apparatus 10 can bemounted to any suitable point in the infrastructure of a building (notshown), for example a wall. This is useful with the present system sincea comparison circuit is provided to determine whether an incoming signalis simply due to extraneous mechanical vibration such as that whichwould be encountered from aircraft, heavy traffic, internal vibration,etc. In this manner, once the natural frequency of the building isdetermined, this can be preset by the potentiometer circuit andtherefore when an incoming signal is less than this frequency, the logicof the circuit, numeral 50 in FIG. 4, can then compare that incomingsignal with the predetermined natural frequency of the structure todetermine whether, in fact, the value is sufficient to actuate the alarm60. In prior art devices, no such comparison circuit has been providedand further, the systems did not provide full electronic components, butrather relied upon electromechanical arrangements or straight forwardmechanical arrangements, all of which are susceptible to temperaturefluctuations, sensitivity limitations, etc. By incorporating alldiscrete electronic components in the apparatus of the presentinvention, no such limitations exist. This is particularly complementedby the fact that the circuit prevents false alarms and can, in fact, beset to “filter out” extraneous vibration to only result in passage ofP-waves, the precursors of S-waves.

A particularly attractive advantage with the present arrangement is thatthe comparator logic circuit 50 is not continuously running forcomparing ground vibration to P-wave vibration as is a chief limitationin the prior art arrangement. With the present invention, once a voltagereaches the threshold value between detector circuit 48 and logiccircuit 50, then the arrangement is actuated. Accordingly, there is nocontinuous power drain with the current arrangement and this, of course,inherently leads to a more reliable and efficient circuit.

In a particularly preferred embodiment, the apparatus 10 may be combinedwith any known sensing means. The sensing means can be placed in anyposition within a room in order to confirm the signal between theapparatus 10 and any such sensing mechanism. In t his manner, theapparatus 10 and the second sensing mechanism can both confirm that thesignal received by the apparatus 10 is, in fact, indicative of animminent earthquake. Transmission between the second sensing mechanismand apparatus 10 may be achieved by any known method, i.e. infra-redtransmission, microwave, etc. In order to facilitate a companion betweenthe two signals, a comparison circuit may be employed. Such circuits arewell known and set forth in the prior art. Once the signal has beencompared, there can be a determination of the signal strength which mayor may not be sufficient to trigger the alarm. Providing thisarrangement, the advantage of preventing false alarms is greatlyenhanced over arrangements in the prior art. The second sensingmechanism may include any number of existing sensors, including uni- ortriaxial sensors, and will be understood that this explanation is notconfined to only a single unit.

A further embodiment is shown in FIG. 7. In this version, a stand-aloneunit 200 comprises a sensor 202, a filter 204, timer 208, controller 210and alarm 212. These elements are all connected within a housing, notshown. The filter permits the passage of signals detected by the sensorhaving a frequency indicative of P-waves. The timer 208 assesses theduration of the selected signals. The controller 210 assesses thevoltage of the signal, indicative of the amplitude of the detectedvibration, and triggers the alarm 212 when the duration and amplitude ofa selected signal exceeds predetermined minimums. For most locations,the minimum duration of concern is about 15 milliseconds.

According to a further embodiment of the present invention, once thesignal determination has been made and the P-wave frequency has beendetected, this information may be relayed via a transmitter to remotelylocated sensors in other buildings or in other geographical areas. Itwill be appreciated by those skilled in the art that transmission of thesignal may be achieved by any of the known methods currently employedfor signal transmission, including telecommunications, Internet, etc.

FIG. 5 sets forth an overall flow chart scheme for providing signalverification and the remotely located relay or transmission of thesignal.

A further embodiment of the invention is illustrated schematically inFIG. 6. Dual sensors 100 and 102 are provided, for mounting to a solidsurface such as a building wall at separate locations removed from eachother, for example on opposing sides of a building or within twoseparate buildings. Each sensor incorporates a transducer-type vibrationdetection means, for converting vibratory movement into an electronicsignal, as described above. Sensors 100, 102 are associated withtransmitters 104 and 106 for transmitting signals from the sensors viawired or wireless communications, including infrared, radio frequency orvisible light frequency. Alternatively, the signals may be transmittedby wire, and the transmitters in this case comprise simply plug-ins forinstallation of a wire. The signals transmitted by tile transmitters arereceived by corresponding receivers 106 & 108, associated with aprocessing unit 120. The processing unit 120 may comprise a stand aloneunit, or alternatively may be integrated with one of the sensors 100 or102 and hardwired to the corresponding sensor. From each receiver 106and 108, the electronic signals are transmitted through a correspondingband pass filter 110, 112. The two band pass filters are used on thereceiver side in order to distinguish the two transmitters, based on(frequency modulated) carrier signals. A suitable band pass filter ismodel ML2110 from MicroLinear (TM). In one example, the firstsensor/filter combination is tuned to 4.7 Kilohertz and the secondsensor/filter combination is tuned to 2.9 kilohertz. Each band passfilter is associated with a corresponding timer circuit and clock unit114, 116. The timer circuit and clock units perform two functions.First, they are adapted to filter out signals having a duration lessthan a preselected duration. For example, it has been found for mostlocalities that tremors are indicative of an impending significantearthquake if they have an amplitude greater than a selected level(indicative of P-waves) with this amplitude peak having a duration ofgreater than approximately 15 milliseconds. If the amplitude peak isless than this, a significant earthquake is not indicated. It has beenfound that this duration may differ in different localities around theglobe, depending on soil type and other factors. Accordingly, adjustmentmeans are provided to change the cut off duration depending on theregion where the device is installed. A further function of the timercircuit/clock unit is to correlate, and compare voltage peak informationwith similar information from corresponding units, as is discussedbelow.

The signal comparison circuit 118 receives signals from the timercircuit/clock units 114 and 116. The signal comparison circuit performsthe function of assessing any temporal overlap in signals received fromthe respective timer circuit/clock units and as well contains apotentiometer circuit for comparing the frequency of the incoming signalwith the natural predetermined frequency of the building as discussedabove. Further, the signal comparison circuit assesses the amplitude ofthe voltage peak of the incoming frequencies, indicative of theamplitude of the detected vibration signal.

The alarm confirmation logic circuit 130 receives from the signalcomparison circuit 118 information regarding the voltage peak amplitude,duration and duration of any temporal overlap between signals receivedfrom the two sensors, and compares this information with a preselectedalarm level. In the event that the amplitude and duration of a signalpeak and duration of overlap between signals received from the twosensors exceeds the preselected level, the alarm 134 is triggered.

A data storage unit 140, which may be remote from the signal comparisonunit 118 or associated therewith, receives data from the signalcomparison unit 118 for storage and later viewing by the user. Data fromthe data storage unit 140 may be downloaded to a computer by way of anRS232 port or any other suitable computer connection means. Computer 144can further process the data, and in particular can compare historicaldata relating to tremors, with any data relating to a tremor received ata given time by the apparatus. This information permits the user tofurther adjust the apparatus to respond to local condition and preventfalse alarms. Further, tile computer 144 may be linked to other similarapparatuses in remote locations via telecommunication means.

A further feature of the present invention resides in the capability ofemploying the sensors as described above in any location, without therequirement of a separate transducer for response to local conditions.For this purpose, the filters 110 and 112 and the various logic circuitsare adjustable, whereby the cut off frequency above which vibrationsignals are not processed may be changed by the user along with theprescribed frequency duration preselected by the user.

FIG. 8 illustrates a variation of this apparatus, wherein the mastercontrol unit 300 incorporates a third sensor 302, linked directly to athird filter 304. This version provides enhanced sensitivity.

The multiple sensors may be mounted in separate buildings or otherstructures, and individually hard-wired to the controller. The remotepositioning of the sensors in this manner enhances the sensitivity ofthe detector.

Although embodiments of the invention have been described above, it isnot limited thereto and it will be apparent to those skilled in the artto which this intention pertains that numerous modifications anddepartures form part of the present invention in so far as they do notdepart from the spirit, nature and scope of the claimed and describedinvention.

What is claimed is:
 1. A method for detecting vibration signals from a stationary object or objects, said signals being indicative of an impending earthquake, characterized by the steps of: providing first and second sensors for detecting vibration within a structure responsive to vibration of a fixed substrate upon which the sensor is mounted, said sensors each featuring an electronic detection circuit to convert said vibration to electronic signals, and a transmitter to transmit said electronic signals via transmission means; providing a processing unit having receiving means for receiving electronic signals transmitted by said sensors, a timer circuit for measuring the duration of the signals received from said sensors, and a logic circuit including a potentiometer circuit; mounting said first and second sensors to said fixed structure; determining the natural vibration frequencies of said structure; presetting said potentiometer circuit to said vibration frequencies of said structure; comparing electronically with said logic circuit any extraneous vibration signal different from said preset vibration frequencies of said structure and allowing passage of electronic signals indicative of P-waves acting on said structure; measuring with said timer circuit the duration and temporal overlap of said signals indicative of P-waves from each of said sensors; determining whether said duration and temporal overlap of said extraneous signals exceed predetermined levels indicative of an impending earthquake; and activating alarm means when said duration and temporal overlap indicate an impending earthquake.
 2. A method as in claim 1 wherein said electronic signals are transmitted from said sensors to said processing unit by means of infrared signal transmission means.
 3. A method as in claim 1 wherein said electronic signals are transmitted from said sensors to said processing unit by means of radio frequency transmission means.
 4. A method as in claim 1 wherein said electronic signals are transmitted from said sensors to said processing unit by means of microwave transmission means.
 5. A method as in claim 1 wherein said electronic signals are transmitted from said sensors to said processing unit by means of visible light transmission means.
 6. A method as in claim 1 characterized by the further step of processing said signals within said processing unit with first and second band pass filters associated with respective sensors, to permit transmission signals from said respective sensors to be separately processed within said processing unit.
 7. A method as in claim 1 wherein electronic signals from said processing unit are downloaded to a computer for further information processing.
 8. A method as in claim 1, comprising the further step of determining the amplitude of said signals with said sensors, and activating said alarm means when said amplitude exceeds a selected level for said selected duration.
 9. A method as in claim 1, comprising the further step of providing a third sensor associated with said processing unit.
 10. A method as defined in claim 1, wherein said alarm means comprises an audible alarm.
 11. A method as defined in claim 1, comprising the further step of actuating a gas supply cutoff means upon detecting earthquake vibration signal.
 12. A method as defined in claim 1, comprising the further step of actuating an elevator interruption means upon detecting said earthquake vibration signal.
 13. A method as defined in claim 1, comprising the further step of actuating fueling operation cutoff means upon detecting said earthquake vibration signal.
 14. An electronic detector for detecting vibration signals of a stationary structure or structures positioned on a substrate and having one or more natural vibration frequencies, and determining whether said vibration signal is a P-wave signal, characterized by: first and second sensors each having a vibration detecting transducer for detecting vibration of said stationary structure and converting said vibration into electronic signals corresponding with the frequency of said vibration; transmission means associated with each of said sensors for transmitting said electronic signals; filter means for selecting signals indicative of the natural vibration frequencies of the structure while permitting passage of signals indicative of P-waves; a processing unit having receiving means for receiving and separately processing said electronic signals; signal comparison means within said processing unit for comparing the duration and temporal overlap between said electronic signals indicative of P-waves to verify whether said signals exceed a selected amount indicative of an impending earthquake.
 15. Apparatus as in claim 14 further characterized by a timer circuit within said processing unit for measuring the duration of said P-wave signals from the respective sensors.
 16. Apparatus as in claim 14 further characterized by alarm means for activation when the duration of said selected signals from each of said sensors is greater than said preselected amount and there exists temporal overlap between said selected signals.
 17. Apparatus as in claim 14 further characterized by potentiometer signal adjustment means for adjusting said sensors to filter one or more selected vibration signals of said structure.
 18. Apparatus as in claim 14, wherein said timer circuit includes adjustment means to adjust the selected signal duration in accordance with local conditions.
 19. Apparatus as in claim 14, wherein said processing unit includes a data downloading port for connection to a computer.
 20. Apparatus as in claim 14 wherein said sensor and processing unit communicate by means of infrared signal transmission.
 21. Apparatus as in claim 14, wherein said sensors and processing unit communicate by means of radio frequency communication.
 22. Apparatus as in claim 14, wherein said sensors and processing unit communicate by means of microwave transmission means.
 23. Apparatus as in claim 14, wherein said sensors and processing unit communicate by visible light transmission means.
 24. Apparatus as in claim 14 wherein said sensors each include multiple laser-based light emitting diodes and said processing unit includes detectors, for transmission of said electronic signals from said sensors to said processing unit.
 25. Apparatus as defined in claim 14, further characterized by amplitude selection means to filter out signals indicative of a vibration amplitude less than a selected level, and wherein said signal comparison means measure only the duration and temporal overlap of signals selected by said amplitude selection means greater than said selected level.
 26. Apparatus as defined in claim 14, further characterized by third sensor means associated with said processing unit.
 27. An apparatus as defined in claim 14, further comprising an audible alarm means for activation upon detection of said P-wave.
 28. An apparatus a defined in claim 14, further comprising a gas supply cutoff means, actuated upon detection of said P-wave.
 29. An apparatus as defined in claim 14, further comprising elevator interruption actuation means, actuable upon detection of said P-wave.
 30. An apparatus as defined in claim 14, further comprising fueling operation cutoff means, actuable upon detection of said P-wave. 